Using an electric mixer, beat the butter and sugar until creamy and smooth,
about two minutes. Add the lemon juice, zest and vanilla and beat well.

In a bowl, combine the flour, poppy seeds, and salt. Add the dry ingredients
to the butter mixture and mix until combined. Form the dough into a disk and,
wrap in plastic wrap and chill for at least 3 hours and up to 3 days or freeze
for up to 2 months.

Preheat oven to 300° F. Roll the dough between two sheets of wax paper to
a 1/4-inch-thick rectangle. return dough to refrigerator for an additional
30 minutes. Cut the shortbread into shapes with a two-inch cookie cutter, or
use a knife, and place 1 inch apart on parchment-lined baking sheets. Do not
reroll scraps, if using cookie cutter. Prick shortbread with a fork and bake
until pale golden all over, 23 to 25 minutes. Cool on a wire rack.